The present disclosure provides layer-by-layer compositions comprising a plurality of polymer bilayers. Each bilayer comprises a poly(N-vinylpyrrolidone) hydrogen-bonded a polyphenol (tannic acid) layer. In the compositions, at least one poly(N-vinylpyrrolidone) has conjugated thereon a plurality of manganoporphyrin moieties. The layer-by-layer compositions can be deposited on the cell aggregate surface or deposited on an underlying surface such as that of a silica core which, when removed creates a capsule having a hollow space for the addition of such as a therapeutic agent.
